1. Field of the Invention
This invention relates generally to a micro-electro-mechanical (MEM) mirror, and more particularly, to a method of linearizing the mirror""s internal position sensor based on driver linearity.
2. Description of the Prior Art
A MEM mirror consists of a small reflective surface with a means for adjusting the angle of the reflective surface relative to the fixed base in which it is mounted. In this system the means for detecting the angle of rotation may be located in close proximity to the mirror itself, possibly contained within the package holding the mirror. It may be implemented for instance using four light emitting diodes (LEDs) surrounding a photo-detector located behind the mirror. This mechanism for detecting rotational position is herein after referred to as the internal feedback sensor.
The internal feedback sensor used in a MEM mirror has inherent non-linearities. These non-linearities adversely affect the mirror movement control system. These non-linearities are especially troublesome when using feedback to move the mirror from one angular location to another (hereto referred to as seeks), because they change the gain in the middle of a mirror adjustment. Such non-linearities can also change the apparent gain when seen at different angles that affects the ability to hold the mirror substantially still (tracking) as well.
In view of the foregoing, it would be both desirable and advantageous in a micro-electro-mechanical (MEM) mirror assembly to provide a technique that reduces or eliminates the non-linearities associated with the internal feedback sensor.
The present invention is directed to a technique that reduces or eliminates the non-linearities associated with the internal feedback sensor used in a micro-electro-mechanical (MEM) mirror assembly. Using the relatively linear response of the mirror positioning motor, the associated driver electronics, and the mirror itself, a calibration is performed that compensates for the internal feedback sensor non-linearity. An expected position can then be calculated simply by multiplying the gain of the system by a given output, due to the good inherent linearity in the system. The calibration will compare measured versus expected position criteria for a predefined set of constant outputs. The data will form a look-up table that will be used to correct for the sensor non-linearities.
In one aspect of the invention, a technique that reduces or eliminates the non-linearities associated with the internal feedback sensor used in a micro-electro-mechanical (MEM) mirror assembly is implemented to provide faster settling times with less overshoot and stalls when performing seeks.
In another aspect of the invention, a technique that reduces or eliminates the non-linearities associated with the internal feedback sensor used in a micro-electro-mechanical (MEM) mirror assembly is implemented to enhance consistency associated with tracking performance.
In yet another aspect of the invention, a technique that reduces or eliminates the non-linearities associated with the internal feedback sensor used in a micro-electro-mechanical (MEM) mirror assembly is implemented in a manner that does not rely on external hardware to perform measurements.
According to one embodiment, a method of linearizing a micro-electro-mechanical (MEM) mirror position sensor comprises the steps of providing a MEM mirror, a mirror position sensor having a non-linear response, and a mirror position control system; tabulating mirror position sensor signals in response to a plurality of desired mirror positions; and adjusting a mirror position control system such that the tabulated mirror position sensor signals are adjusted to have a linear relationship to the plurality of desired mirror positions.
According to another embodiment, a method of linearizing a micro-electro-mechanical (MEM) mirror position sensor comprises the steps of providing a MEM mirror and a mirror position control loop having a non-linear mirror position sensor; tabulating non-linear mirror position sensor signals in response to a plurality of desired mirror positions; and adjusting the tabulated non-linear mirror position sensor signals such that the mirror position control loop provides a linear response to the non-linear mirror position sensor signals.
According to yet another embodiment, a micro-electro-mechanical (MEM) mirror positioning system comprises a MEM mirror; a non-linear mirror position sensor; and a controller configured to adjust output signals generated via the non-linear mirror position sensor such that the controller operates to provide a linear mirror position response to the output signals generated via the non-linear mirror position sensor.